A. Field of the Invention
This invention relates to improved hydrocarbon fuels which prevent or reverse the octane requirement increase (ORI) phenomenon conventionally observed during the initial portion of the operating life of spark-ignition internal combustion engines.
The octane requirement increase (ORI) effect exhibited by internal combustion engines, e.g. spark ignition engines, is well known in the art. This effect may be described as the tendency for an initially new or clean engine to require higher octane quality fuel as operating time accumulates, and is coincidental with the formation of deposits in the region of the combustion chamber of the engine. Thus, during the initial operation of a new or clean engine, a gradual increase in octane requirement (OR), i.e. fuel octane number required for knock-free operation, is observed with an increasing buildup of combustion chamber deposits until a rather stable or equilibrium OR level is reached which, in turn, seems to correspond to a point in time where the quantity of deposit accumulation on the combustion chamber and valve surfaces no longer increases but remains relatively constant. This so-called "equilibrium value" is usually reached between about 3,000 and 20,000 miles or corresponding hours of operation. The actual equilibrium value of this increase can vary with engine design and even with individual engines of the same design: however, in almost all cases the increase appears to be significant, with ORI values ranging from about 2 to 10 research octane numbers (RON) being commonly observed in modern engines.
It is also known that additives may prevent or reduce deposit formation, or remove or modify formed deposits, in the combustion chamber and adjacent surfaces and hence decrease OR. Such additives are generally known as octane requirement reduction (ORR) agents.
B. Description of the Prior Art
The use of oil soluble aliphatic polyamines containing at least one olefinic polymer chain to improve detergent properties of fuel and lubricant compositions is disclosed in a number of patents including U.S. Pat. Nos. 3,275,554; 4,438,757; 3,565,804; 3,574,576; 3,898,056; 3,960,515; 4,022,589 and 4,039,300, and their disclosures are incorporated by reference.
Further, a number of patents have issued relating to the use of cyclomatic manganese compounds to make improvements in gasoline compositions including U.S. Pat. Nos. 2,818,417; 2,839,552 and 3,127,351, and their disclosures are incorporated herein by reference. U.S. Pat. No. 3,127,351 discloses that fuel compositions containing the disclosed manganese compounds provide significant reduction in ORI in both leaded and unleaded fuels, generally at levels up to 6.0 grams of manganese per gallon. It has recently been suggested that use of such manganese compounds particularly at higher concentrations results in increased levels of certain undesirable materials such as hydrocarbons in the exhaust gas from the engine than is produced using solely unleaded fuels. There is evidence that use of such manganese compounds at very low levels, e.g. about 0.10 gram per gallon or less do not materially contribute to the undesirable emission characteristics of the spark ignited engines using them, however, neither are they particularly effective in inhibition or prevention of octane requirement increase.